Motorcycle rear suspension swingarm assembly

ABSTRACT

An off-road motorcycle incorporating a swingarm assembly for pivotally supporting a rear wheel relative to a main frame portion of the motorcycle. Preferably, the swingarm includes right and left arms extending rearwardly from a forward connecting portion. Right and left rear wheel mount members are secured to the right and left arms, respectively, to rotatably support the rear wheel of the motorcycle. Preferably, the arms from the swingarm assembly are formed at least partially by a hydroforming process wherein the center of the arms has a width that is greater than the width of either a forward or rearward end of the arm. In addition, the forward ends of each of the right end left arms are bent inward such that the forward portion of the swingarm assembly is narrower than the rear portion of the swingarm assembly. Desirably, the hydroforming process permits the inner wall of the arms to be vertical and substantially planar, even along the region where the arms are bent. In addition, a vibration absorbing coating is applied to the wheel support members in a manner to be interposed between an inner surface of the wheel support members and the outermost portion of a hub of the rear wheel.

PRIORITY INFORMATION

This application is related to, and claims priority from, JapanesePatent Application No. 2001-185807, filed on Jun. 20, 2001, the entiretyof which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to vehicle suspension systems. Moreparticularly, this invention relates to a rear suspension swingarmassembly for supporting a rear wheel of the motorcycle.

2. Description of the Related Art

Motorcycles generally include an engine supported within a cradle-typeframe assembly. A typical arrangement includes a front suspension forkassembly supported by the frame for rotation about a steering axis. Thefork assembly supports a front wheel of the motorcycle at its lower end.A handlebar assembly is mounted to the suspension fork to permitsteering of the front wheel of the motorcycle. An elongated,straddle-type seat assembly is typically supported above the frame. Arear wheel of the motorcycle is commonly supported by a suspensionswingarm assembly, which is pivotally supported by, and extends in arearward direction from, a lower portion of the frame. Thus, both thefront and rear wheels are typically suspended for limited, controlledmovement along a suspension travel path relative to the frame.

A common swingarm assembly includes a connecting portion, which istypically connected to the motorcycle frame and to which one end of asuspension member, such as a hydraulic shock absorber, is mounted. Oneor more tubular arms typically extend in a rearward direction from theconnecting portion. A rear wheel of the motorcycle is often supported ata rearward end of the arm(s).

In a common arrangement, a hub assembly of the rear wheel is rotatablysupported on a shaft, or axle, which is carried by the swingarmassembly. An intermediate member, such as a washer, for example, may bepositioned between the hub and an inner surface of the swingarmassembly. A nut is often threaded on one end of the axle and tightenedto secure the hub on the axle and to press the hub (and washer, ifprovided) firmly against the inner surface of the swingarm.

However, vibrations transmitted from the engine, along with forcesimparted on the rear wheel when traversing rough terrain, nonethelessresult in a slight amount of relative movement between the hub, orwasher, and the swingarm. The friction produced from this relativemovement tends to wear the inner surface of the swingarm assembly. Overtime, such wear may compromise the strength or stiffness of the swingarmassembly. Accordingly, this region of the swingarm assembly may beenlarged to compensate for the impending wear. The size increase,however, disadvantageously adds weight to the assembly.

SUMMARY OF THE INVENTION

Accordingly, a preferred embodiment inhibits wear of the inner surfaceof the swingarm assembly caused by relative movement between the hubassembly (including any intermediate members) and the swingarm assembly.In one arrangement, a vibration absorbing coating is applied to at leasta portion of the swingarm assembly that may come into contact with thehub assembly or any intermediate component placed therebetween. Inanother arrangement, a rear wheel support member is affixed to arearward end of each of the one or more arms of the swingarm assembly.At least a portion of the inner surface of the wheel support member(s)that may come into contact with the hub assembly or any intermediatecomponent placed therebetween includes a coating of a vibrationabsorbing material. In some arrangements, the entire wheel supportmember(s), or even the entire swingarm assembly, may be coated with avibration absorbing material.

One aspect of the present invention involves an off-road motorcyclecomprising a frame. A front suspension assembly is rotatably supportedby the frame and rotatably supports a front wheel. A rear swingarmassembly is pivotably supported by the frame and rotatably supports arear wheel. An internal combustion engine is supported by the frame andis configured to drive the rear wheel. The swingarm assembly includes atleast one elongated, tubular arm extending along a side of the rearwheel in a direction substantially aligned with a vertical, centralplane of the motorcycle. The arm has a rearward end portion arranged toreceive an axle configured to support a hub assembly of the rear wheel.The end portion has an inner surface facing the hub assembly. The innersurface has a first portion and a second portion defining a contactsurface arranged to contact a portion of the hub assembly. The secondportion is spaced from the first portion toward the hub assembly todefine a thickened area of the end portion.

Another aspect of the present invention involves an off-road motorcyclecomprising a frame and a front suspension assembly rotatably supportedby the frame. The front suspension assembly rotatably supports a frontwheel. A rear swingarm assembly is pivotably supported by the frame androtatably supports a rear wheel. An internal combustion engine issupported by the frame and is configured to drive the rear wheel. Theswingarm assembly comprises at least one elongated, tubular armextending along a side of the rear wheel in a direction substantiallyaligned with a vertical, central plane of the motorcycle. The arm has arearward end portion arranged to receive an axle configured to support ahub assembly of the rear wheel. The end portion has an inner surfacefacing the hub assembly, wherein a portion of the inner surfacecontacting the hub comprises a lubricious layer.

Still another aspect of the present invention involves a rear suspensionswingarm assembly for an off-road motorcycle. The swingarm assembly isconfigured to be pivotably supported by a frame of the motorcycle androtatably support a rear wheel of the motorcycle. The swingarm assemblyincludes a connecting portion defining a pivot axis of the swingarmassembly relative to the frame of the motorcycle. In addition, theswingarm assembly includes a first elongated, tubular arm and a secondelongated, tubular arm. Each of the first and second arms is fixed tothe connecting portion and extend along a side of the rear wheel. Eachof the arms has a rearward end portion arranged to receive an axleconfigured to support a hub assembly of the rear wheel. The end portionhas an inner surface facing the hub assembly and having a thickenedportion extending toward the hub assembly.

A further aspect of the present invention involves a rear suspensionswingarm assembly for an off-road motorcycle. The swingarm assembly isconfigured to be pivotably supported by a frame of the motorcycle androtatably support a rear wheel of the motorcycle. The swingarm assemblyincludes a connecting portion defining a pivot axis of the swingarmassembly relative to the frame of the motorcycle. The swingarm assemblyadditionally includes a first elongated, tubular arm and a secondelongated, tubular arm. The first and second arms are fixed to theconnecting portion and extend along a side of the rear wheel. Each ofthe arms has a rearward end portion arranged to receive an axleconfigured to support a hub assembly of the rear wheel. The end portionhas an inner surface facing the hub assembly, wherein a portion of theinner surface contacting the hub comprises a vibration absorbingcoating.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will be described with reference to drawings of a preferredembodiment, which is intended to illustrate, and not to limit, thepresent invention. The drawings comprise 19 figures.

FIG. 1 is a side elevational view of an off-road motorcycleincorporating a preferred rear suspension swingarm assembly that isconnected to a frame.

FIG. 2 is a top plan view of the rear suspension swingarm assembly ofFIG. 1. The swingarm assembly includes a forward connecting portion,right and left arms extending rearwardly from the connecting portion andright and left wheel mount members fixed to rearward ends of the arms.

FIG. 3 is a left side view of the rear swingarm assembly of FIG. 2viewed in a direction of the arrow 3 of FIG. 2.

FIG. 4 is a right side view of the swingarm assembly of FIG. 2 as viewedin a direction of the arrow 4 of FIG. 2.

FIG. 5 is a cross-sectional view of the swingarm assembly of FIG. 2taken along the view line 5—5 of FIG. 2. FIG. 5 a is a view of aleft-side access member taken along the view line 5 a—5 a of FIG. 5 andFIG. 5 b is a view of a right-side access member taken along the viewline 5 b—5 b of FIG. 5.

FIG. 6 is a side view of a forward portion of the swingarm assembly anda related portion of the motorcycle frame. An upper end of a rear shockabsorber is connected to the motorcycle frame and a lower end of therear shock absorber is connected to the swingarm assembly through alinkage arrangement.

FIG. 7 is a cross-sectional view of a connection between a forwardportion of the swingarm assembly and the motorcycle frame, taken alongthe view line 7—7 of FIG. 6.

FIG. 8 is a cross-sectional view of a rear portion of the swingarm and ahub assembly associated with a rear wheel of the motorcycle of FIG. 1.The view is taken along the view line 8—8 of FIG. 1. A rear brakecaliper is shown in phantom lines.

FIG. 9 is a schematic view of a preferred mold arrangement for use inproducing the arms of the swingarm assembly of FIG. 2.

FIG. 10 is a top plan view of the left wheel mount member of the rearswingarm assembly of FIG. 2 incorporating a vibration absorbing coating.

FIG. 11 is a side view of the left wheel mount member taken in adirection of the arrow 11 of FIG. 10.

FIG. 12 is an enlarged view of a portion of the left side of the rearswingarm assembly and rear wheel hub assembly indicated by the view line12 of FIG. 8, which view illustrates the vibration absorbing coating.

FIG. 13 is a top plan view of a modification of the swingarm assembly ofFIG. 2.

FIG. 14 is a top plan view of a right rear wheel mount member of theswingarm of FIG. 13 incorporating a vibration absorbing member.

FIG. 15 is a side view of an inner side of the right rear wheel mountmember taken in a direction of the arrow 15 of FIG. 14.

FIG. 16 is a top plan view of a left side rear wheel mount member of theswingarm assembly of FIG. 13 incorporating a vibration absorbing member.

FIG. 17 is a side view of an inner side of the left rear wheel mountmember taken in a direction of the arrow 17 of FIG. 16.

FIG. 18 is a side view of the vibration absorbing member of FIG. 16.

FIG. 19 is a partial cross-sectional view of the vibration absorbingmember taken along the view line 19—19 of FIG. 18.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 1, an off-road motorcycle incorporating apreferred rear suspension swingarm assembly is identified generally bythe reference numeral 20. The motorcycle 20 includes a frame assembly 22that is formed primarily from tubular members, which may have circularor other suitable cross-sectional configurations.

The frame assembly includes a head pipe 23. A front suspension forkassembly 24 is journaled for rotation with respect to the frame assembly22. In particular, the front suspension fork assembly extends throughthe head pipe 23 of the frame assembly 22. A handlebar assembly 26 iscarried at an upper end of the front fork assembly 24 and can be used tosteer a front wheel 28, which is rotatably journaled at a lower end ofthe fork assembly 24 in any suitable manner. The front fork assembly 24also supports a front fender 30 at a position above the front wheel 28.The front fender 30 is arranged to deflect dirt, mud or other debristhat may be thrown upward by the front wheel 28.

A lower, rearward portion of the frame assembly 22 pivotally supports arear swingarm assembly 32. The swingarm 32 supports a rear wheel 36 ofthe motorcycle 20 at its rearward end. Preferably, the swingarm 32 isformed of aluminum or a similar alloy such that the overall weight ofthe swingarm can be reduced. In addition, as will be explained below,the swingarm 32 is designed to further reduce the overall weight of theswingarm.

A rear shock absorber 38 is operably connected between the frameassembly 22 and the rear swingarm assembly 32. Preferably, the rearshock 38 is connected to the swingarm 32 through a linkage arrangement40, as is described in greater detail below. Thus, the rear shockabsorber 38 provides resistance to articulating (i.e., pivotal) movementof the swingarm assembly 32 and the rear wheel 36. The linkage assembly40 may be utilized to alter a leverage ratio between the rear wheel 36and the shock absorber 38. In an alternative arrangement, the shockabsorber 38 may be connected directly to the swingarm 32 and the linkageassembly 40 can be omitted.

The frame 22 also supports a rear fender 42 at a position above the rearwheel 26. The rear fender 42 is arranged to deflect mud, dirt or otherobjects that may be thrown in an upward direction by the rear wheel 36.

The frame assembly 22 supports a fuel tank 44 in a position generallybehind and below the handle bar assembly 26. Desirably, the fuel tank 44surrounds and extends below at least a portion of the frame assembly 22,which somewhat lowers the center of gravity of the motorcycle 20.

A straddle-type seat assembly 46 extends between the fuel tank 44 andthe rear fender 42. Desirably, the seat assembly 46 has a relativelyflat upper surface, which advantageously permits a rider of themotorcycle 20 to move relatively freely between various positions alongthe length of the seat assembly 46. Such operator movement is greatlydesired during off-road operation of the motorcycle 20, for instance.

The frame assembly 22 also supports an internal combustion engine 50. Inthe illustrated arrangement, the frame assembly 22 forms a cradle-likestructure in which the engine 50 is supported. Preferably, the engine 50is positioned below the fuel tank 44 and seat assembly 46 to provide themotorcycle 20 with a relatively low center of gravity, which improvesthe handling characteristics of the motorcycle 20.

The illustrated engine 50 operates on a two-stroke, crankcasecompression principle and is of a single cylinder arrangement. However,other suitable engine arrangements may also be used, such as amulti-cylinder arrangement or an engine configuration that operates onother operating principles, such as a four-stroke engine, for example.

Preferably, a chain and sprocket drive assembly 52 extends between theengine 50 and the rear wheel 36 and is configured to transfer torqueproduced by the engine 50 to the rear wheel 36. The chain, thus,transfers power from the engine 50 to the rear wheel 36 to propel themotorcycle 20 in a manner well known in the art. Although a chain andsprocket type drive assembly 52 is illustrated, other suitable types ofdrive arrangements may also be used, such as a belt drive or shaft drivearrangement, for example.

With reference to FIG. 2, the rear swingarm assembly 32 is illustratedwith certain components of the motorcycle 20 removed for clarity.Desirably, the rear swingarm assembly 32 is generally in the shape ofthe letter “H” in top plan view and defines a forward space S1 toaccommodate a portion of the rear shock absorber 38 and a rearward spaceS2 to accommodate the rear wheel 36 of the motorcycle 20. In someapplications, the forward space S1 can be omitted and the shock absorber38 will not extend below the swingarm assembly 32; however, by allowingthe shock absorber 38 to connect at a location under the swingarmassembly 32, the travel of the rear swingarm assembly 32 can beincreased, which is very desirable in off-road applications.

As described above, a forward end of the swingarm assembly 32 isconfigured to be pivotally connected to the frame assembly 22 of themotorcycle 20 and a rearward end of the swingarm assembly 32 isconfigured to rotatably support the rear wheel 36. Desirably, the rearswingarm assembly 32 is substantially symmetrical about a vertical,central plane CP, which passes through the length of the motorcycle 20.Other arrangements of the swingarm assembly 32 are also possible. Forexample, the swingarm assembly 32 may be single-sided, i.e., extendalong only one side of the rear wheel; however, the substantiallysymmetrical design provides better handling and balance to themotorcycle, which is used in off-road applications.

The illustrated swingarm assembly 32 includes a forward connectingportion 60, which serves to connect the swingarm assembly to the frameassembly 22 of the motorcycle 20. Preferably, a forward portion 61 ofthe right arm 62 and a forward portion 63 of the left arm 64 are securedto the connecting portion 60. More preferably, the forward portions 61,63 are welded to the connecting portion 60. The welded connection helpsreinforce the arms 62, 64 in a forward portion of the arms 62, 64.

In the illustrated arrangement, the forward portions 61, 63 and theconnection portion extend alongside each other and the top and bottomare welded together along a seam that is defined by the two longitudinalsurface that are placed in abutment. Other suitable techniques also canbe used to secure the components together. Advantageously, the forwardportions 61, 63 are disposed generally forward of a forwardmost portionof the rear wheel 36. Such a placement facilitates attachment locationbetween the arms 62, 64 and the connecting portion 60.

The right arm 62 and the left arm 64 preferably extend rearwardly fromthe connecting portion 60 on opposing sides of the central plane CP.When viewed from the rear of the motorcycle 20, the right arm 62 ispositioned on the right side of the central plane CP and the left sidearm 64 is positioned on the left side of the central plane CP. In someapplications, a single side arm can be used instead of the generallyparallel arms 62, 64 and the single side arm can extend from the frameand alongside the rear wheel 36.

The arms 62, 64 preferably are formed in a unitary structure. In otherwords, the arms 62, 64 preferably are not cut, or generally machinedsuch that the cross-section of the arms 62, 64 desirably are not changedby cutting, machining or welding. More preferably, the arms 62, 64 havea generally rectangular tubular shape that is formed throughhydroforming, which will be described below. Even more preferably, thearms 62, 64 are formed by hydroforming an elliptical or oval shapedtube. While other constructions are possible, as discussed above in theSummary of the Invention, the unitary construction advantageouslyimproves the structural integrity of the arms 62, 64.

A right wheel support member 66 is connected to the rearward end of theright arm 62 and a left wheel support member 68 is connected to therearward end of the left arm 64. Preferably, the right and left wheelsupport members are formed by a forging technique to produce a rigid andstrong component. The right and left wheel support members 66, 68cooperate to support an axle 70 (FIG. 8), which, in turn, supports a hubof the rear wheel 36 of the motorcycle 20. The axle 70 preferablycomprises a head at one end and a nut 71 at the other end. In theillustrated arrangement, a forward portion 67 of the right wheel supportmember 66 is inserted into the generally open rear face of the right arm62 and welded therein. Similarly, a forward portion 69 of the left wheelsupport member 68 is inserted into the generally open rear face of theleft arm 64 and welded therein.

Right and left extensions 72, 74 of the forward connecting portion 60extend in a direction substantially parallel to the center plane CPalong opposing sides of the forward space S1 and terminate in right andleft mounting portions 76, 78, respectively. The extensions 72, 74desirably are arcuate in top plan view (see FIG. 2). The arcuate designhelps reduce stress risers and improves the structural integrity of therear swingarm assembly 32.

The right and left mounting portions 76, 78 each include a cylindricalaperture 80, 82, respectively, extending in a direction substantiallynormal to the central plane CP. Centerlines of the apertures 80, 82 arealigned and cooperate to define a pivot axis AP of the swingarm assembly32. The apertures 80, 82 are configured to receive a support shaft,which connects the swingarm assembly 32 to the frame 22, as is describedin greater detail below.

A bridge portion 84 of the forward connecting portion 60 extends betweenthe right and left arms 72, 74 and, desirably between forward endportions of the right arm 62 and the left arm 64 of the swingarmassembly 32. The bridge preferably is arcuate in top plan view such thatstress risers can be reduced and the strength of the bridge portion canbe improved. Desirably, the bridge portion 84, right and left arms 72,74 and right and left mounting portions 76, 78 are formed from a unitarypiece of material such that the forward connecting portion 60 is onecontinuous piece. Preferably, the forward connecting portion 60 is castfrom an aluminum alloy, however, other suitable methods of manufacturingand materials may also be used.

The bridge portion 84 advantageously connects the right and leftportions of the swingarm assembly 32 in an intermediate position alongthe total length of the swingarm assembly 32, thereby improving thestructural integrity of the rear swingarm assembly 32. In a preferredarrangement, the arms 62, 64 are welded to the connecting portion 60. Insome less advantageous arrangements, the arms 62, 64 are formedintegrally with the right and left arms 72, 74 respectively and theright and left mounting portions 76, 78 respectively, with the bridge 84being welded between the two portions.

As illustrated in FIG. 2, the extensions 72, 74 of the forwardconnecting portion 60 are closer to one another, in a direction normalto the center plane CP, than at least the rearward ends of the arms 62,64. In other words, the forward end of the swingarm assembly 32 isnarrower than a rearward portion of the swingarm assembly 32. Inaddition, the outer walls of the extensions 72, 74 are concave whichdefines right and left clearance spaces 86, 88 on outboard sides of theright and left arms 72, 74 of the forward connecting portion 60. Thesespaces 86, 88 advantageously provide extra clearance for the heels of arider of the motorcycle 20 or provide space for other components of themotorcycle 20 to be positioned. These spaces 86, 88 also areadvantageously positioned at a location along the swingarm assembly thatis reinforced by the bridge portion 84 and that is subjected torelatively lower loading due to its proximity to the pivot axis AP. Inone arrangement, a master cylinder of a rear brake assembly (not shown)may be positioned in the space 86. Other components also can be disposedwithin this region.

In order to place the extensions 72, 74 closer to each other relative torearward portions of the arms 62, 64, both the right and left arms 62,64 are bent at an intermediate location, or region IR, between theforward and rearward ends of the arms 62, 64 such that the forward endsof the arms 62, 64 are located further inward than the rearward ends inthe assembled swingarm 32. Although the illustrated bend, and theassociated intermediate region IR, is located at approximately a centralportion along the length of the arms 62, 64, in other arrangements thelocation of the bends may be varied. For example, the bend may belocated to create clearance for a specific type or size of rear wheel36.

Preferably, an inner, vertical surface 62 a, 64 a of the arms 62, 64that is located at the bend, or within the intermediate region IR, issubstantially planar. That is, the surfaces 62 a, 64 a (see FIGS. 2 and9) preferably do not bow in or out. More preferably, the surfaces 62 a,64 a also are substantially vertical. As a result, the strength andstiffness of the arms 62, 64 is improved, thus permitting the wallthickness of the arms 62, 64 to be minimized, resulting in a low overallweight. The forming of the inner surfaces 62 a, 64 a is described ingreater detail below.

The swingarm assembly 32 in general and, specifically, the right andleft arms 62, 64 are advantageously sized and shaped to provide thedesired strength and stiffness in order to achieve desirable handlingcharacteristics of the motorcycle 20, while keeping the weightadvantageously low. Preferably, the right and left arms 62, 64 define afirst width, in a direction generally normal to the central plane CP,within the intermediate region IR. Preferably, the width W1 is greaterthan a width W2 of the arms 62, 64 at a forward end and is also greaterthan the width W3 of the arms 62, 64 at a rearward end. As described ingreater detail below, such an arrangement optimizes thestrength-to-weight ratio of the swingarm assembly 32.

With reference to FIGS. 3 and 4, left and right sides, respectively, ofthe swingarm assembly 32 are shown. Preferably, each of the right andleft arms 62, 64 define a first vertical dimension, or height H1, at aposition approximately one-third of the length of the arms 62, 64 fromthe forward ends thereof. More preferably, the first vertical dimensionH1 is disposed roughly adjacent to a juncture of the arms 62, 64 and thebridge member 84. Moreover, the height HI preferably is disposed in aregion of the arms 62, 64 in which an opening is provided for an accessmember 130, 134, which are described below.

In addition, each of the arms 62, 64 preferably define a second verticaldimension, or height H2, near rearward ends of the arms 62, 64. Becausegreater strength is required near the middle portion, or intermediateregion IR, of the swingarm assembly 32, the height H1 is desirablygreater than the height H2. The height of the arms 62, 64 preferablygradually changes from H1 to H2 along the length of the arms 62, 64 suchthat stress localization can be reduced. Such an arrangement serves toimprove the overall strength-to-weight ratio of the swingarm assembly 32over prior arrangements.

Each of the right and left wheel mount members 66, 68 define an aperture90, 92, respectively, extending transversely therethrough. The apertures90, 92 are elongated along the length of the swingarm 32 and areconfigured to receive the rear wheel axle 70 (FIG. 8). The elongatedapertures 90, 92 permit the rear wheel 36 to be moved forward orrearward a limited distance, in a direction substantially parallel tothe central plane CP, to permit the tension of the drive chainarrangement 52 to be adjusted, as is well known in the art.

A protruding wall 91 extends outward from the right wheel mount member66 and a protruding wall 93 extends outward from the left wheel mountmember 68. The walls 91, 93 extend in a generally C-shaped manner aboutthe apertures 90, 92 respectively.

With reference to FIGS. 5 and 6, the shock absorber 38 and linkagearrangement 40 is described in greater detail. As discussed previously,the rear shock absorber 38 desirably is connected to the swingarmassembly 32 through a linkage arrangement 40. In the illustratedarrangement, a lower portion of the shock absorber 38 is connected tothe swingarm assembly 32 at a location generally between the forwardportions 61, 63 of the right and left arms 62, 64. An upper portion ofthe shock absorber 38 is connected to the frame assembly 22.

The shock absorber 38 preferably is capable of providing both a springforce and a damping force to influence the articulating movement of theswingarm assembly 32 and, thus, the rear wheel 36. Desirably, the shockabsorber includes a cylinder portion 94 and a rod portion 96. An upperend 98 of the cylinder portion 94 desirably is connected to the frame 22of the motorcycle 20 while a lower end 100 of the rod portion 96 isconnected to the linkage arrangement 40. A suspension spring 102 isoperably positioned between the cylinder portion 94 and the rod portion96 and provides a biasing force that tends to separate the cylinderportion 94 from the rod portion 96.

Preferably, a piston (not shown) is mounted to an upper end of the rodportion 96 and divides a fluid chamber (not shown) within the cylinderportion 94 into a compression chamber and a rebound chamber on oppositesides of the piston. A reservoir body 104 can be connected to the shockabsorber 38 to define a reservoir chamber (not shown), which is in fluidcommunication with the compression chamber of the shock absorber 38. Afloating piston may separate the reservoir chamber of the reservoir body104 from a gas chamber, which exerts a pressure on the fluid within thereservoir chamber, as is well known in the art.

Upon compression motion of the shock absorber, a portion of the fluidwithin the compression chamber may move through a compression circuit ofthe shock absorber 38 while the remaining portion of the fluidcompression chamber may move into the reservoir chamber. Upon reboundmotion of the shock absorber 38, fluid moves through a rebound circuitof the shock absorber 38 from the rebound chamber back into thecompression chamber. In addition, fluid from the reservoir chamber alsoreturns to the compression chamber. Although such a shock absorber 38 ispreferred, other suitable types of shock absorbers may also be used.

As described above, the lower end of the shock absorber 38 is connectedto the swingarm assembly 32 through a linkage arrangement 40.Specifically, a generally “L-shaped” link member 110 is connected to thelower portion 100 of the shock absorber 38 at a first end and connectedto the swingarm assembly 32 at a second end. A swing link member 112 isconnected to a lower portion (not shown) of the motorcycle frame 22 at afirst end and is connected to an intermediate portion of the link member110 at its second end. Preferably, the swing link 112 is comprised oftwo arms (FIG. 5) positioned on either side of the lower end 100 of theshock absorber 38. However, other suitable swing link arrangements mayalso be used.

As illustrated in FIG. 5, desirably, an upper end of the link member 110is connected to the swingarm assembly 32 and, specifically, to thebridge portion 84, by a bolt 114. The upper end extends up into a recessformed in the connecting portion 60 (i.e., the bridge portion 84) and issecured by the bolt 114. The bolt 114 includes a shaft portion 116,which rotatably supports the link member 110. Desirably, a bushingarrangement 118 is positioned between the link 110 and the shaft 116 ofthe bolt 114. However, a bearing arrangement, such as a needle bearingor roller bearing arrangement, may also be used. The bolt 114 includes ahead portion 120 on one end, which has a larger diameter than the shaftportion 116. A nut 122 is threaded to the opposing end of the bolt 114thereby securing the link 110 to the swingarm 32. While a bolt isillustrated, other suitable mechanical connections also can be used.Preferably, one side of the head portion 120 is flat to form a face thatabuts a portion of the connecting portion 60 to keep the bolt 114 fromrotating when installed.

Similarly, a bolt 124 secures the swing link 112 to the link member 110.Desirably, a bushing arrangement 126 is positioned between the bolt 124and the link member 110, in a manner substantially similar to thatdescribed immediately above. In both cases, a set of seals preferably ispositioned at the outer ends of the bushing arrangements 118, 126. Theseals reduce the dust, dirt and grime that may wear the bushingarrangements 118, 126 prematurely.

A hollow, cylindrical access member 130 extends through the right arm 62and a portion of the bridge 84 of the swingarm assembly 32 and defines acavity which permits access to the nut 122. Desirably, the access member130 is generally circular in cross section. Other suitableconfigurations also can be used. A plug 132, which may be made of rubberor a similar flexible material, desirably closes the outer end of theaccess member 130 to reduce the likelihood that water, dirt, dust andother foreign matter will enter the access member 130.

Similarly, an access member 134 passes through the left arm 64 and aportion of the bridge 84 of the swingarm assembly 32 to provide accessto the head 120 of the bolt 114. However, the access member 134desirably includes a flat along a portion of its perimeter, whichcooperates with a corresponding flat 138 of the bolt head 120 to preventthe bolt 120 from turning relative to the swingarm 32. A plug member 140is desirably positioned within the open end of the access member 134 toprevent water, dirt, dust and other foreign material from entering theaccess member 134.

The differentiated access members 130, 134 can assist a mechanic,operator or other person in locating the side with the removable nut 122in the illustrated arrangement. In addition, by utilizing the accessmembers 130, 134 the length of the bolt 114 could be reduced because thebolt did not have to extend completely through both of the arms 62, 64.

With reference to FIG. 7, as described above, a forward end of theswingarm 32 is rotatably connected to the frame 22 of the motorcycle 20to pivot about a pivot axis AP (FIG. 6). Specifically, a bolt 142includes a shaft portion 144, which passes through apertures 146, 148 ofthe frame 22 and supports the portions 76, 78 of the swingarm 32. Inaddition, the shaft portion 144 of the bolt 142 additionally passesthrough an aperture 150 of a rearward end of a body portion of theengine 50. A nut 152 may be threaded to an end of the bolt 142 to secureit in place.

With reference to FIG. 8, a hub portion of the rear wheel 36 is shown insection. As described above, a rear axle 70 passes through the elongatedapertures 90, 92 of the swingarm assembly 32 and rotatably supports therear wheel 36. Specifically, a hub 160 is supported on the axle 70 by apair of bearings 162 positioned near the outer ends of the hub 160. Theillustrated bearings 162 are sealed bearing assemblies utilizing aplurality of individual ball bearing members. However, other suitablebearing arrangements may also be used. In the illustrated arrangement, aseal 163 is disposed on the outside of each of the bearings 162 toreduce the likelihood that water, dust, dirt and the like can work intothe area between the hub portion of the rear wheel 36 and the rear axle70.

A pair of outer spacers 164 space the bearings 162 from the right andleft arms 66, 68, respectively, of the swingarm assembly 32 while anintermediate spacer 166 spaces the bearings 162 apart from one another.A pair of seal assemblies 168, which include the seals 163, inhibitwater, dust, dirt, or other foreign material from coming into contactwith the bearings 162.

The hub 160 supports a rear sprocket 170 of the chain drive arrangement52, desirably near its left end. A roller-type chain 172 engages teethon the sprocket 170 to drive the rear wheel 36 in a manner well known inthe art. Near its right end, the hub 160 supports a disc brake rotor 174such that the disc brake rotor 174 will rotate with the rear wheel 36. Arear brake caliper 176 (FIG. 8, shown in phantom lines) is supported bythe swingarm 32 and is configured to selectively engage the rotor 174 toimpart a stopping force on the rear wheel 36, as is well known in theart. As can be appreciated, the rotor 174 and the sprocket 170 can bereversed relative to each other and, in some applications, can bepositioned on the same side of the wheel, if desired.

The right wheel mount member 66 of the swingarm assembly 32 defines aninner, generally planar surface 180. Preferably, an intermediate member,such as washer 182, is positioned between the surface 180 and the brakecaliper 176. The intermediate member 182 assists in inhibiting damage tothe surface 180 during operation of the motorcycle 20.

Similarly, the left wheel mount member 68 of the swingarm assembly 32defines an inner, generally planar surface 184. An intermediate member,such as washer 186, desirably is positioned between the surface 184 andthe spacer 164 to inhibit damage to the surface 184. The wheel mountmembers 66, 68 are described in greater detail below.

With reference to FIG. 2, as described above, the width of the arms 62,64 of the swingarm assembly 32 vary along the length of the arms 62, 64to optimize the strength to weight ratio of the swingarm assembly 32.Advantageously, the arms 62, 64 define a width W1 in a central portionthereof which is greater than a width W2, W3 of either end of the arms62, 64. Such an arrangement allows the swingarm 32 to resist deflectionat its central portion, where loads are the greatest, while maintaininga relatively low weight. The central portion with the width W1preferably is just rearward of the location at which the arms 62, 64 arecoupled to the coupling member 60. The widths preferably graduallychange from W2 to W1 to W3 along the length of the arms. The gradualchange in widths reduces stress localizing that can occur at drasticchanges in width.

Desirably, the arms 62, 64 are formed to their final shape and size, atleast in part, by a hydroforming process. In such a process, the arms62, 64 are initially elongated tubular members, or workpieces, having anelliptical cross-section. The workpieces are cut to approximately theirfinal length and are bent into approximately their final shape. Thetubular member is then placed within a die cavity having an interiorsurface sized and shaped in the desired final size and shape of theouter surface of the arm members 62, 64. The die is closed and a bladderis placed within the center of the tubular workpiece. Fluid is thenintroduced into the bladder and pressurized to a level sufficient toexpand the workpiece until it conforms to the internal surface of thedie cavity, thus forming the final shape of the arms 62, 64.

Such an arrangement permits the arm members 62, 64 to be constructedwith a width W2, W3 at the ends thereof to be less than a width W1 ofthe central portion of the arms 62, 64. This is because, once deflated,the bladder can be easily removed from the arm members 62, 64, unlikethe solid internal die used in a swaging process.

In addition, such a method of construction allows the inner surfaces62A, 62B of the arms 62, 64 to remain vertical and substantially planaralong their length and especially at the intermediate region IR whereinthe arms 62, 64 are bent inward. As described above, with conventionalmanufacturing methods the bent portions of the arms 62, 64 are deformedupon manufacture into a vertical concave shape (i.e., the center portionof the inside vertical face caves inward), which compromises thestrength and stiffness of the arms and requires more material to beadded in order to provide the desired amount of strength and stiffness.This results in a heavier swingarm assembly.

With reference to FIG. 9, the left arm 64 of the swingarm assembly 32 isshown in section with a desired, general location of a parting line L ofthe hydroforming die illustrated schematically. As illustrated,desirably the hydroforming die is configured such that the two halves ofthe die separate along the parting line L, which extends atapproximately a 45-degree angle from a vertical plane defined by theinner surface 64 a. In addition, the parting line L desirably extendsfrom an upper, inside corner of the arm 64 (i.e., an intersection of theinner surface 64 a and upper surface 64 b) and, on the opposing side ofthe arm 64, extends from a lower, outside corner (i.e., an intersectionof the outer surface 64 c and lower surface 64 d).

Such an arrangement permits an upper, outer comer 192 and a lower, innercomer 190 of the arm 64 to have a continuously rounded surface. Incontrast, the other two comers of the arm 64 from which the parting lineL extends may have a surface imperfection along the line L where the twohalves of the hydroforming die meet. The stresses in the arm 64undesirably concentrate at such an imperfection. With the illustratedarrangement, the comer 190 subjected the greatest amount of stress andthe comer 192 that is most readily visible when the arm 64 is assembledto the motorcycle 20 are free from surface imperfections to bothimproved the strength and improve the appearance of the arm 64.

With reference to FIGS. 10 through 12, the left wheel mount member 68 isillustrated in greater detail. Although not separately illustrated, theright wheel support member 66 is desirably constructed in a mannersubstantially similar to that described below in relation to the leftwheel support member 68.

Desirably, a forward end 193 of the wheel support member 68 is sized andshaped to fit within an open, rearward end of the arm 64. Preferably,the wheel support member 68 is welded to the arm 64 to secure it inplace. However, other suitable constructions and arrangements may alsobe used. For example, the wheel support member 68 may be formed from thesame piece of material as the arm 64. Alternatively, threaded fasteners,or the like, may be used to secure the wheel support member 68 to thearm 64.

Desirably, the wheel support member 68 includes a protrudingreinforcement portion 194 substantially annular in shape and surroundingthe elongated aperture 92. The reinforcement portion 194 forms a portionof the inner surface 184 of the wheel support member 68 and, desirably,is sized and shaped to contact the washer 186 when the axle 70 and rearwheel 36 is at any position within the elongated aperture 92. With suchan arrangement, the reinforcement portion 194 creates a thickened wallportion of the wheel mount 68 to better withstand forces applied to themount member 68 while simultaneously maintaining a low weight.

With reference to FIG. 12, desirably, the wheel support member 68includes a coating 196, which is interposed between the contact surface184 and the washer 186. The coating 196 can comprise a solid lubricant,such as molybdenum disulphide system fluororesin. The coating 196 mayalso comprise either a lubricant or a vibration absorbing material, suchas rubber or an elastomeric material, or both, and preferably covers atleast the reinforcement portion 194. The coating layer 196 preferably isabout 35+/−5 μm in regions that contact other components and about 15 μmelsewhere. Alternatively, however, the entire wheel support member 68may be coated. In such arrangements, the remainder of the swingarmassembly 32 preferably is processed with a surface treatment, such as ananodized or aluminum anodic coating, such as ALUMITE. Further, in somearrangements, it may be desirable to coat the entire swingarm assembly32 with the vibration absorbing material 196. In one configuration, thewasher 186 is coated rather than the reinforcement portion 194 becausethe washer can be more readily replaced when the coating is worn away.

With such an arrangement, vibration between the washer 186 and the wheelsupport member 68 is absorbed by the coating 196 and prevents damage tothe surface of the wheel support member 68 that would otherwise occurdue to relative motion therebetween. Accordingly, such an arrangementprovides the swingarm assembly 32 with a longer usable life.

FIGS. 13 through 19 illustrate a modification of the swingarm assembly32 of FIGS. 1 through 12 and is referred to generally by the referencenumeral 32′. The swingarm assembly 32′ is substantially similar to theswingarm assembly 32 described above and, therefore, like referencenumerals will be used to describe like components except for a prime (′)that has been added.

As illustrated in FIGS. 14 and 15, the modified rear wheel supportmember 66′ includes a reinforcement portion 200′ that, desirably, isconstructed from a separate piece of material from the remainder of thesupport member 66′ and, when assembled, forms a portion 184 a′ (FIG. 15)of the inner surface 184′ that is in contact with the washer 186. Suchan arrangement permits the reinforcement portion 200′ to be coated witha vibration absorbing material, as described above, separately from theremainder of the wheel support member 66′. Thus, manufacturing issimplified and, if necessary, the reinforcement portion 200′ may beeasily replaced.

With reference to FIG. 14, desirably, the reinforcement portion 200′ isreceived within a recess formed by an inner surface of the supportmember 66′. That is, only approximately one-half of the thickness of thereinforcement portion 200′ is exposed beyond the inner surface 184 b′(FIG. 15) surrounding the reinforcement portion 200′. Such anarrangement permits the reinforcement portion 200′ to be securely heldin a desired position with a minimum of fasteners.

Preferably, at least a rearward end of the reinforcement portion 200′ isfixed to the wheel support member 66′ by one or more fasteners.Desirably, the reinforcement portion 200′ includes a pair of countersunkapertures 202 (only one shown), which cooperate with a pair of threadedapertures 204 (only one shown) of the wheel support member 66′ toreceive a pair of threaded fasteners 206 to secure the reinforcementportion 200′ to the wheel support member 66′.

With reference to FIGS. 16 through 19, the left wheel support portion68′ desirably also includes a separate reinforcement portion 194′secured thereto. The left reinforcement portion 194′, desirably, isconstructed substantially identically to the reinforcement portion 200′described immediately above. Thus, the reinforcement portion 194′ isreceived within a recess of the wheel support portion 68′ and alsoincludes a pair of countersunk apertures 210 which cooperate with a pairof threaded apertures 212 to receive a threaded fastener 214 and therebysecure the reinforcement portion 194′ to the wheel support member 68′.

Although the present invention has been described in the context ofpreferred embodiments, it is not intended to limit the invention to theprovided example. Modifications to the above-described swingarm assemblyapparent to one of skilled in the art are considered to be part of thepresent invention. Accordingly, the invention should be defined solelyby the appended claims.

1. An off-road motorcycle comprising a frame, a front suspensionassembly rotatably supported by the frame and rotatably supporting afront wheel, a rear swingarm assembly pivotably supported by the frameand rotatably supporting a rear wheel, an internal combustion enginesupported by the frame and being configured to drive the rear wheel, theswingarm assembly comprising at least one elongated, tubular armextending along a side of the rear wheel in a direction substantiallyaligned with a vertical, central plane of the motorcycle, the swingarmassembly having a rearward end portion member mounted to the tubular armand arranged to receive an axle, the axle being configured to support ahub assembly of the rear wheel, the end portion having an inner surfacefacing the hub assembly, the inner surface having a first portion and asecond portion, the second portion defining a contact surface arrangedto directly contact a portion of the hub assembly and being spaced fromthe first portion toward the hub assembly to define a thickened area ofthe end portion, which is thicker than a thinner area defined by thefirst portion.
 2. An off-road motorcycle comprising a frame, a frontsuspension assembly rotatably supported by the frame and rotatablysupporting a front wheel, a rear swingarm assembly pivotably supportedby the frame and rotatably supporting a rear wheel, an internalcombustion engine supported by the frame and being configured to drivethe rear wheel, the swingarm assembly comprising at least one elongated,tubular arm extending along a side of the rear wheel in a directionsubstantially aligned with a vertical, central plane of the motorcycle,the arm having a rearward end portion arranged to receive an axle, theaxle being configured to support a hub assembly of the rear wheel, theend portion having an inner surface facing the hub assembly, the innersurface having a first portion and a second portion, the second portiondefining a contact surface arranged to contact a portion of the hubassembly and being spaced from the first portion toward the hub assemblyto define a thickened area of the end portion, wherein the contactsurface comprises a dry lubricant material.
 3. The motorcycle of claim2, wherein a remainder of the swingarm assembly is coated with analuminum anodic coating.
 4. The motorcycle of claim 1, additionallycomprising an annular member fixed to an inner surface of the endportion, the annular member defining the second portion of the innersurface.
 5. An off-road motorcycle comprising a frame, a frontsuspension assembly rotatably supported by the frame and rotatablysupporting a front wheel, a rear swingarm assembly pivotably supportedby the frame and rotatably supporting a rear wheel, an internalcombustion engine supported by the frame and being configured to drivethe rear wheel, the swingarm assembly comprising at least one elongated,tubular arm extending along a side of the rear wheel in a directionsubstantially aligned with a vertical, central plane of the motorcycle,the arm having a rearward end portion arranged to receive an axle, theaxle being configured to support a hub assembly of the rear wheel, theend portion having an inner surface facing the hub assembly, the innersurface having a first portion and a second portion, the second portiondefining a contact surface arranged to contact a portion of the hubassembly and being spaced from the first portion toward the hub assemblyto define a thickened area of the end portion, additionally comprisingan annular member fixed to an inner surface of the end portion, theannular member defining the second portion of the inner surface, whereinthe contact surface comprises a dry lubricant material.
 6. Themotorcycle of claim 5, wherein a remainder of the swingarm assembly iscoated with an aluminum anodic coating.
 7. An off-road motorcyclecomprising a frame, a front suspension assembly rotatably supported bythe frame and rotatably supporting a front wheel, a rear swingarmassembly pivotably supported by the frame and rotatably supporting arear wheel, an internal combustion engine supported by the frame andbeing configured to drive the rear wheel, the swingarm assemblycomprising at least one elongated, tubular arm extending along a side ofthe rear wheel in a direction substantially aligned with a vertical,central plane of the motorcycle, the arm having a rearward end portionarranged to receive an axle, the axle being configured to support a hubassembly of the rear wheel, the end portion having an inner surfacefacing the hub assembly, wherein a portion of the inner surfacecontacting the hub comprises a lubricious layer.
 8. The off-roadmotorcycle of claim 7, wherein the at least one arm comprises a firstarm and a second arm, the first and second arms being positioned onopposing sides of the rear wheel.
 9. The motorcycle of claim 7, whereina remainder of the swingarm assembly is coated with an aluminum anodiccoating.
 10. A rear suspension swingarm assembly for an off-roadmotorcycle, the swingarm assembly configured to be pivotably supportedby a frame of the motorcycle and rotatably supporting a rear wheel ofthe motorcycle, the swingarm assembly comprising a connecting portiondefining a pivot axis of the swingarm assembly relative to the frame ofthe motorcycle, the swingarm assembly additionally comprising a firstelongated, tubular arm and a second elongated, tubular arm, each of thefirst and second arms being fixed to the connecting portion andextending along a side of the rear wheel, first and second rearward endportion members mounted to the first and second tubular armsrespectively and arranged to receive an axle, the axle being configuredto support a hub of the rear wheel, each end portion member having aninner surface facing the hub, the inner surface having a first thinnerportion facing the hub and a second thickened portion directlycontacting the hub and extending from the first thinner portion towardthe hub assembly.
 11. A rear suspension swingarm assembly for anoff-road motorcycle, the swingarm assembly configured to be pivotablysupported by a frame of the motorcycle and rotatably supporting a rearwheel of the motorcycle, the swingarm assembly comprising a connectingportion defining a pivot axis of the swingarm assembly relative to theframe of the motorcycle, the swingarm assembly additionally comprising afirst elongated, tubular arm and a second elongated, tubular arm, eachof the first and second arms being fixed to the connecting portion andextending along a side of the rear wheel, each of the arms having arearward end portion arranged to receive an axle, the axle beingconfigured to support a hub assembly of the rear wheel, the end portionhaving an inner surface facing the hub assembly, the inner surfacehaving a thickened portion extending toward the hub assembly, whereinthe thickened portion comprises a contact surface having a lubriciouslayer.
 12. The swingarm assembly of claim 11, wherein a remainder of theswingarm assembly is coated with an aluminum anodic coating.
 13. Theswingarm assembly of claim 10, additionally comprising an annular memberfixed to an inner surface of the end portion, the annular memberdefining the thickened portion of the inner surface.
 14. A rearsuspension swingarm assembly for an off-road motorcycle, the swingarmassembly configured to be pivotably supported by a frame of themotorcycle and rotatably supporting a rear wheel of the motorcycle, theswingarm assembly comprising a connecting portion defining a pivot axisof the swingarm assembly relative to the frame of the motorcycle, theswingarm assembly additionally comprising a first elongated, tubular armand a second elongated, tubular arm, each of the first and second armsbeing fixed to the connecting portion and extending along a side of therear wheel, each of the arms having a rearward end portion arranged toreceive an axle, the axle being configured to support a hub assembly ofthe rear wheel, the end portion having an inner surface facing the hubassembly, the inner surface having a thickened portion extending towardthe hub assembly, additionally comprising an annular member fixed to aninner surface of the end portion, the annular member defining thethickened portion of the inner surface, wherein the contact surfacecomprises a vibration absorbing material.
 15. The swingarm assembly ofclaim 14, wherein a remainder of the swingarm assembly is coated with analuminum anodic coating.
 16. A rear suspension swingarm assembly for anoff-road motorcycle, the swingarm assembly configured to be pivotablysupported by a frame of the motorcycle and rotatably supporting a rearwheel of the motorcycle, the swingarm assembly comprising a connectingportion defining a pivot axis of the swingarm assembly relative to theframe of the motorcycle, the swingarm assembly additionally comprising afirst elongated, tubular arm and a second elongated, tubular arm, thefirst and second arms being fixed to the connecting portion andextending along a side of the rear wheel, each of the arms having arearward end portion arranged to receive an axle, the axle beingconfigured to support a hub assembly of the rear wheel, the end portionhaving an inner surface facing the hub assembly, wherein a portion ofthe inner surface contacting the hub comprises a vibration absorbingcoating.
 17. The swingarm assembly of claim 16, wherein the first andsecond arms are positioned on opposing sides of the rear wheel.
 18. Theswingarm assembly of claim 16, wherein a remainder of the swingarmassembly is coated with an aluminum anodic coating.
 19. A rearsuspension swingarm assembly for an off-road motorcycle, the swingarmassembly configured to be pivotably supported by a frame of themotorcycle and rotatably supporting a rear wheel of the motorcycle, theswingarm assembly comprising a connecting portion defining a pivot axisof the swingarm assembly relative to the frame of the motorcycle, theswingarm assembly additionally comprising a first elongated arm and asecond elongated arm, each of the first and second arms being fixed tothe connecting portion and extending along a side of the rear wheel,each of the arms having a rearward end portion with an aperture arrangedto receive an axle, the axle being configured to support a hub of therear wheel, the end portion having an inner surface facing the hub, theinner surface having a first area extending around the aperture anddefining a hub contact area configured to directly contact the hub, anda second area immediately adjacent to the first area, the second areabeing recessed away from the hub relative to the first area such thatthe first area projects inwardly from the second area toward the hub.20. The rear suspension swingarm assembly as set forth in claim 19,wherein the first area defines a thickened area of the end portion thatis thicker than the second area.
 21. The rear suspension swingarmassembly as set forth in claim 19, wherein the first area extendscompletely around a periphery of the aperture.
 22. The rear suspensionswingarm assembly as set forth in claim 19, wherein the first area isannular in shape.
 23. The rear suspension swingarm assembly as set forthin claim 19, wherein the first area defines a first planar area lying ina first plane and the second area defines a second planar area lying ina second plane, the first plane being disposed closer to the hub thanthe second plane.